1. Technical Field
The present invention relates to a light collecting member, and an optical module and an image reading device having the light collecting member, and, more particularly, to a light collecting member which collects light reflected from an original into a photoelectric conversion element, and an optical module and an image reading device having that.
2. Background Art
Various types of an image reading device which reads an image using a movable optical module are known. FIG. 11 is a perspective view of an ordinary image reading device. FIG. 12 is a perspective view which indicates the inside of the ordinary image reading device. As shown in FIG. 11 and FIG. 12, there is incorporated an optical module 97 in the chassis of an image reading device 99.
FIG. 13 is a perspective view of an ordinary optical module 97. The optical module 97 includes a light source 92, a plurality of mirrors 93 and a lens 91. The light source 92 applies light to an original placed on a platen of the image reading device. The plurality of mirrors 93 lead the light reflected from the original to a CCD (Charge Coupled Device: photoelectric conversion element) which is not illustrated. Meanwhile, the lens 91 is arranged between the mirrors 93 and the CCD, and the lens 91 concentrates the light reflected by the mirrors 93 and makes it form an image on the CCD.
Here, the CCD which is not illustrated is arranged in a CCD substrate 94, and the lens 91 is fixed on a lens bracket 96. The CCD substrate 94 and the lens bracket 96 are fixed on a module bracket 95 which forms the frame of the optical module 97.
A perspective view in the neighborhood of the lens 91 of the optical module 97 is shown in FIG. 14. Also, a perspective view of the lens 91 is shown in FIG. 15, and its side view is shown in FIG. 16. As shown in FIG. 15 and FIG. 16, an ordinary lens tube for the lens 91 is formed into a cylindrical shape. In FIG. 14, the lens 91 and the lens tube of the lens 91 are positioned by the CCD substrate 94 and the lens bracket 96, and further fixed by a lens holding member 98 from above. For example, a method of positioning the lens 91 and the CCD to the optical module is disclosed in patent document 1 (Japanese Patent Application Laid-Open No. 2007-300256) or patent document 2 (Japanese Patent Application Laid-Open No. 1994-43562).
In an ordinary image reading device, light emitted from a light source reflects at a surface of an original and passes the lens 91 via the mirrors 93, and is collected toward the CCD. Here, when ambient light enters a space between the lens 91 and the CCD, an image degrades. In addition, when trash and a foreign particle invade the space between the lens 91 and the CCD, a light beam emitted from the lens 91 is interrupted by the trash and the foreign particle, and an image photoelectrically converted by the CCD differs from the original.
As a method to settle the above-mentioned problem, a technology in which a closed space is formed by a lens-fixing chassis and a CCD substrate, and a lens and a CCD are arranged in the closed space is disclosed in patent document 3 (Japanese Patent Application Laid-Open No. 1997-83736) , for example.